Ink jet printing is a well-known technique by which printing is accomplished without contact between the printing device and the substrate on which the printed characters are deposited. Briefly described, ink jet printing involves the technique of projecting a stream of ink droplets to a surface and controlling the direction of the stream, e.g., electronically, so that the droplets are caused to form the desired printed message on that surface.
The technique of ink jet printing or non-contact printing is particularly well suited for application of characters onto irregularly shaped surfaces, including, for example, glass, metal, or plastic containers, generally used for holding beverage, cosmetic, pharmaceutical, liquor, and health care products.
Reviews of various aspects of ink jet printing can be found in the following publications: Kuhn et al., Scientific American, April, 1979, 162-178; and Keeling, Phys. Technol., 12(5), 196-303 (1981). Various ink jet apparatuses are described in the following U.S. Pat. Nos.: 3,060,429, 3,298,030, 3,373,437, 3,416,153, and 3,673,601.
In general, an ink jet ink composition must meet certain rigid requirements to be useful in ink jet printing operations. These relate to viscosity, resistivity, solubility, compatibility of components and wettability of the substrate. Further, the ink must be quick-drying and smear resistant, resist rubbing, and be capable of passing through the ink jet nozzle without clogging, and permit rapid cleanup of the machine components with minimum effort.
In addition, the ink must meet certain other requirements. Many beverage manufacturers fill the containers with chilled beverages, frequently under humid conditions that promote condensation of moisture on the containers. The moisture that condenses on the container surfaces poses a severe problem in obtaining ink penetration, good adhesion, and abrasion resistance of the printed messages. Thus, the jet ink should allow printing on these containers in the presence of the condensation, and the printed messages should not be damaged by the condensation. Further, when the containers are immersed in ice water for chilling, the messages should not disintegrate or be damaged by the ice water. Moreover, the bottles may be exposed to warm and humid conditions during warehousing and shipping to different parts of the world and in different seasons. The messages should not be damaged by the hot and cold humid conditions. Further, the messages should be removable by a caustic wash in order to allow reuse of the returned glass bottles.
Many of the known ink jet ink compositions are not suitable for printing on glass under humid conditions, or do not provide water resistant printed messages on glass surfaces. Only a few ink compositions are reported to be suitable for printing on glass surfaces under humid conditions. For example, U.S. Pat. No. 5,693,127 discloses a jet ink comprising a binder, a colorant, a liquid vehicle and an adhesion promoter which is an alkoxysilyl polyalkylene-imine. Although the patent states that the ink is suitable for printing on glass bottles having a condensation thereon, certain difficulties are encountered in following its teachings. For example, the alkoxysilyl polyalkylene-imine adhesion promoter does not appear to be commercially available, and the patent does not teach those of ordinary skill in the art how to make this adhesion promoter. Further, the stability of the ink composition containing alkoxysilylated polyalkylene-imines remains uncertain.
U.S. Pat. No. 5,596,027 discloses an ink jet ink composition comprising an ink carrier, a colorant, a polyamine, and an acidic resin. This ink composition is capable of producing condensation and moisture resistance images on glass bottles. Although the claims are directed to solvent-based as well as water-based ink compositions, the patent does not suggest ways of producing ink compositions having the combination of specific advantages, namely, the short drying time, condensation resistance, rub resistance, and alkali washability. It is known that water-based inks take a relatively long time to dry on glass substrates. Drying times greater than 10 seconds may be necessary with water-based inks.
Thus, there exists a need for a jet ink composition meeting certain critical performance requirements. There exists a need for a fast drying jet ink composition that provides high quality messages on container surfaces, especially glass surfaces. There exists a need for a jet ink composition which can be printed on glass surfaces which may have moisture condensation on them. There exists a need for a jet ink composition whose printed messages do not smear, rub off, or otherwise degrade after exposure to ice water. Further, there exists a need for a jet ink composition whose printed messages do not smear, rub off, or otherwise degrade after exposure to hot and cold humid conditions. There further exists a need for a jet ink composition whose printed messages on glass surfaces can be washed off by a caustic solution.
It is therefore an object of the present invention to provide a jet ink composition that provides high quality messages on various surfaces, particularly glass surfaces which may have a condensation of moisture on them. It is a further object of the present invention to provide a jet ink composition whose printed messages do not smear, rub off, or otherwise degrade when exposed to hot and cold humid conditions. It is also an object of the present invention to provide a jet ink composition whose printed messages do not smear, rub off, or otherwise degrade when exposed to ice water. It is a further object of the present invention to provide a jet ink composition whose messages on glass surfaces can be washed off readily using a caustic solution.